The virus that can
cause West Nile encephalitis in humans
is not only found in crows,
according to scientists at the U.S. Geological
Survey's National
Wildlife Health Center in Madison, Wis. USGS has recently
released a
list of 18 bird species that the Centers for Disease Control
and
Prevention(CDC) in Fort Collins, Colo. confirmed as having tested positive
for the West Nile virus, including:

American crow

Ring-billed gull

Yellow-billed cuckoo

Rock
dove

Sandhill crane

Blue jay

Bald
eagle

Laughing gull

Black-crowned night-heron

Mallard

American
robin

Fish crow

Red-tailed hawk

Broad-winged hawk

Cooper's
hawk

Belted kingfisher

American kestrel

Herring gull

"Although the cause of
death has not been determined
in all cases, we can assume that these
birds were exposed to the virus
in the tri-state area of New York, New
Jersey and Connecticut," said
Dr. Robert McLean, USGS wildlife
biologist and director of the Madison
Center. "Some of these
species could play a significant role as we
track the spread of this
disease."

McLean added, "The variety of birds is disturbing
because
many of these species migrate to other areas and could potentially
disseminate the disease elsewhere. The good news is, with the exception
of American crows, there were only a few individual birds from each
respective
species thattested positive. It is still too early to tell
if this is because
they are not as susceptible or they were not as
readily observed as crows."

Monitoring mortality in
American crows is especially
important because crows appear to be
highly sensitive to the virus. Since
many crows normally travel less
than 200 miles they can act as sentinels
for local transmission of the
disease.

"At this time it is difficult to assess how many
birds
have died from this disease. While some of the affected areas have
reported very high bird mortality, especially in crows, a number of the
birds have died from other causes," said USGS wildlife disease
specialist
Linda Glaser. "About 49percent of the 392 birds tested
by the USGS
and CDC have tested positive for West Nile
virus."

McLean and his team of USGS biologists have been taking
blood
samples from migratory and non-migratory birds in the New York area
to
get a sense of the extent that bird populations and various species
were exposed to thevirus. "This information, in addition to being
shared with the CDC, will be used in establishing an effective
surveillance
network to track the virus and ultimately learn how it
could impact our
native bird populations," saidMcLean.

There is still much
that is unknown about the ecology
of the virus and how it will respond
to its new environment in the United
States. "Once a bird is
infected, the virus can be transmitted to
mosquitoes only for about 4
to 5 days. Although this appears to be a short
time, many birds can
migrate hundreds of miles within that time. It will
be important to
find out what species are involved in the transmission
of the virus and
if migratory birds, including crows, are capable of moving
the virus to
new locations,"said McLean.

The USGS will continue to focus
on collecting information
that will help determine the extent of the
wildlife species involved, the
geographic and temporal distribution of
the virus, and whether the disease
is continuing to expand to new
sites.

McLean emphasized that with so many state and federal
agencies
involved in the West Nile investigation, he is optimistic that
scientists will learn what role migratory birds may play in determining
if the West Nile viruswill find a permanent home in the western hemisphere
and what impact it will have on our native species.

Periodically, the USGS issues
Wildlife Health Alerts
to keep natural resource agencies appraised of
wildlife health or disease
issues that may threaten free-ranging and
captive wildlife. USGS, along
with several state and federal and local
natural resource, public and animal
health agencies,is diligently
monitoring the spread of the virus by conducting
field investigations,
processing wildlife specimens, and keeping these
agencies informed
through the USGS Wildlife Health Alerts.

The USGS is also developing
digital maps to monitor the
expansion and range of the disease. The
maps can be quickly updated and
allow scientists to electronically
overlay maps showing other pertinent
information such as climate,
vegetation, bird and mosquito species range
for the area being
studied.

West Nile virus is closely related to St. Louis encephalitis
virus, but generally causes a milder disease in humans, according to
information
from the CDC. The West Nile virus is transmitted by a
mosquito, which acquires
the virus when it bites an infected bird for
the blood meal needed toproduce
mosquito eggs. If the same mosquito
subsequently bites a human, it can
pass the virus to a human host. Like
St. Louis encephalitis, West Nile
virus is not transmitted directly
from person to person or from birds to
persons. This is the first time
West Nile virus has been recognized in
the United States or any other
area of the Western Hemisphere.

As the nation's largest water, earth and biological science
and
civilian mapping agency the USGS works in cooperation with more than
2000 organizations across the country to provide reliable, impartial,
scientific
information to resource managers, planners, and other
customers. Thisinformation
is gathered in every state by USGS
scientists to minimize the loss of life
and property from natural
disasters, contribute to sound economic and physical
development of the
nation's natural resources, andenhance the quality of
life by
monitoring water, biological, energy, and mineral resources.

Note: This story has
been adapted from a news release
issued by U.S. Geological Survey for
journalists and other members of
the public. If you wish to quote from
any part of this story, please credit
U.S. Geological Survey as the
original source. You may also wish to include
the following link in any
citation: http://www.
sciencedaily.com/releases/1999/11/991118075040.htm